1. Field of the Invention
The present invention relates to a developing roller to be incorporated into an apparatus adopting an electrophotographic mode such as a copying machine, a printer, or a receiving apparatus of a facsimile, to an electrophotographic process cartridge, and to an electrophotographic image forming apparatus.
2. Description of the Related Art
In a copying machine, facsimile, or printer employing an electrophotographic mode, a photosensitive member is charged by charging unit and then an electrostatic latent image is formed on the photosensitive member by laser. Next, a developer in a developer container is conveyed by a developer carrying member, and then the electrostatic latent image on the photosensitive member is developed with the developer at a portion where the photosensitive member and the developer carrying member are close to each other.
After that, the developer on the photosensitive member is transferred onto recording paper by transferring unit, and is then fixed by heat and a pressure. A developing roller of such a construction that an elastic layer is provided on the periphery of a metal mandrel and one or more surface layers are formed thereon as required, or a developing sleeve free of any elastic layer has been used as the developer carrying member. Particularly in an electrophotographic apparatus according to a non-magnetic, one-component contact development mode, the developing roller having the elastic layer has been suitably used, and a silicone rubber excellent in deformation recoverability and softness has been widely used as a constituent material for the elastic layer.
Such developer carrying member serves to provide charge for the developer through triboelectric charging as well as to convey the developer. The charged state of the developer largely affects the image quality and stability of an electrophotographic image. Accordingly, the developer carrying member has been demanded to be capable of controlling the charged state of the developer to a proper one. In particular, an insufficient charge quantity of the developer is responsible for the occurrence of, for example, fogging in the electrophotographic image. Accordingly, the developer carrying member has been demanded to improve its triboelectric charge-providing performance for the developer.
Japanese Patent Application Laid-Open No. H03-192377 discloses a method involving adding a copolymer containing a quaternary ammonium base to the surface layer of a developing roller for improving its charge-providing performance for a negatively chargeable developer.
In addition, Japanese Patent Application Laid-Open No. 2010-170105 discloses a method involving adding a copolymer containing a quaternary ammonium base to the surface layer of a developing sleeve for improving its charge-providing performance for a negatively chargeable developer.
By the way, the triboelectric charge quantity of a developer tends to reduce as the temperature or humidity of an environment surrounding the developer increases. Meanwhile, the variety of environments where an electrophotographic image forming apparatus is used has started to increase extremely.
In view of the foregoing, the inventors of the present invention have acknowledged that a developer carrying member capable of stably charging a developer even under a high-temperature, high-humidity environment, specifically, for example, an environment having a temperature of 40° C. and a relative humidity of 90% is needed.
Under such acknowledgement, the inventors of the present invention have conducted an investigation on the addition of such copolymer containing a quaternary ammonium base as described in each of Japanese Patent Application Laid-Open No. H03-192377 and Japanese Patent Application Laid-Open No. 2010-170105 listed above to the surface layer of a developer carrying member having a silicone rubber elastic layer.
As a result, the inventors have confirmed that the developer carrying member shows good charge-providing performance for a negatively chargeable developer even under a high-temperature, high-humidity environment. However, when the member is stored under the high-temperature, high-humidity environment for a long time period, adhesiveness between the surface layer and the silicone rubber elastic layer reduces, and hence the surface layer peels off the silicone rubber elastic layer in some cases.
That is, the inventors have acknowledged that high adhesiveness for the silicone rubber elastic layer as well as high charge-providing performance is needed for the surface layer of the developer carrying member using the silicone rubber elastic layer.